[ARC5] APX-6 IFF

[Tim]

Hi Mike - good stuff!  I have not played with any IFF gear but I have
played with my APR-4 receiver.  It works pretty well.  What I've learned
about it and how it works today, here if you're bored:
https://www.n6cc.com/an-apr-1-apr-4-radar-comm-surveillance-receiver/

73, Tim
N6CC

On Fri, Dec 16, 2022 at 11:03 AM <mstangelo at comcast.net> wrote:

> The APX-6 and APR-4 brings back fond memories of my first and only foray
> into Microwave operation.
>
> I read about the APX-6 in the surplus catalogs and found out there was an
> article in September 1960 and February 1961 issues of QST. I wrote to the
> VHF Editor of QST at the time, E.P. Tilton W1HDQ, about getting copies of
> the articles. He sent back a typewritten replay on ARRL stationary (I still
> have the letter) that he was the author and will send me copies of the
> articles.
>
> I received the articles but was intimidated with the installation of the
> coax connectors on the anode and cathode transmitter cavities so I put the
> project on hold. In the February 1968 issue of QST I saw a letter
> describing another method providing the feedback by soldering inductance
> straps in the cathode cavity. I wrote and author Jim, W0PFP, asking details
> about the installation. I received a reply on a memo with an Iowa State
> University letterhead from Jim detailing the location of the straps.
> Apparently Jim worked in the Department of Electrical Engineering. (I also
> kept this memo).
>
> I bought two APX-6 from BC Electronics in Chicago and did the IF strip and
> cavity mods. I built a dipole on an HN connector and checked out the
> transmitter by listening to the signal in a APR-4 receiver I picked up at a
> hamfest. Listening on a receiver I heard pulses which I found out years ago
> were from the ADS aircraft transponder. I tested the set's range in my
> parent's yard which was 200 feet long but did not to any further operation
> because by Ham friends weren't into experimentation. I forgot what I did
> with those sets.
>
> Years later I mentioned the sets to an office worker who was in the Air
> Force stationed in Thailand during the Vietnam War. He remembers working on
> the KY encoders but had no memories the RF IFF unit.
>
> Mike N2MS
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